The present paper focuses on developing a cost-risk evaluation model in order to evaluate the risk of cost that may happen in project stages. Since, it is important to detect risk factors which may cause cost overrun for different activities and stages of various projects; the main objective is to provide an evaluation method in order to determine the current value of cost risks in construction projects. Risk cost may occur in different stages of construction and the time value of money is different over the construction time, it is necessary to have a detailed assessment between the risk categories. For this purpose, the project is broken to stages and activities and the cost of activities, cost risk factors, activity cost risk, stage cost risk, total value of project cost risk and so on are determined. Eventually, the present value of cost risk, the value of different risk groups are calculated and compared to three pre-defined risk categories.